Small airway abnormalities have been pointed out in cases of interstitial lung diseases in several papers, however, others have reported that those may be due to the effect of smoking in such patients. In the present study, small airways were histologically and physiologically evaluated in 24 cases of various interstitial lung diseases. Biopsy specimens revealed peribronchiolar fibrosis in 18 cases and smooth muscle hypertrophy and thickening of basement membrane in 15 cases. However, existence and degree of airway narrowing could not be evaluated in our biopsy specimens. Pulmonary function data showed restrictive changes in most of the cases with normal FEV1.0% and RV/TLC. Comparing normal smokers and nonsmokers, V50 and V25 were decreased in 14 cases and 13 cases, respectively, and closing volume was elevated in 12 out of 19 cases in interstitial lung diseases. Relations of V50 and V25 to vital capacity were not significant, therefore, reduction of V50 and V25 could not be attributed to the decrease in lung volume.
These results indicate that the small airway diseases are common in interstitial lung diseases.
